1. Field of the Invention
This invention relates generally to multilayer plastic containers. More specifically, the invention relates to improved multilayer plastic containers having at least three layers, one of the layers providing oxygen and CO2 barrier protection which are useful for holding and storing beverages
2. Background Art
Multilayer containers having a layer of oxygen barrier material such as EVOH are well known in the art. EVOH also provides a CO2 barrier protection which is useful for storing and holding carbonated beverages. Such multilayer containers are blown from preforms. The preforms are manufactured by a multilayer injection molding process such as the process described generally in U.S. Pat. No. 4,511,528 which is incorporated by reference herein. One problem in manufacturing such injection molded preforms is the control of the flow of various materials.
It is desirable to make containers having an inner and outer layer of PET and a middle layer of EVOH for products requiring oxygen and CO2 barrier protection such as carbonated beverages. EVOH is a relatively expensive material and is much more expensive than the PET used to make the inner and outer layers of the container. Accordingly, multilayer containers having a layer of EVOH for oxygen and CO2 barrier protection have generally only been used with products that require a relatively thin layer of EVOH, approximately 0.5 to 1 mils. The preforms from which these generally known containers are made have a layer of EVOH of approximately 4-10 mils.
Containers having thicker layers of EVOH, approximately 2-3 mils, are generally thought to be cost prohibitive when compared with other types of containers due to the cost of the EVOH. Preforms for making such containers must contain a layer of EVOH which is approximately 20-30 mils thick. Additionally, the difficulty of controlling such relatively thicker layers of EVOH is more difficult than controlling relatively thin layers of EVOH. If the EVOH flow is not accurately controlled in making the preform, the layer of EVOH is not evenly distributed in the blown container. Thus, the EVOH may become exposed to the inner or outer surfaces of the bottle. If EVOH is exposed to either of these surfaces, expensive EVOH is wasted. Furthermore if EVOH is exposed to the inner or outer surfaces of the containers the EVOH can flake away from the bottle creating an undesirable appearance for a consumer. Additionally, if the EVOH is unevenly distributed around the bottom profile of the container, it can cause weaknesses in the bottom profile which can make the bottle unstable and subject to deformation from internal pressures.
It is one of the principal objectives of the present invention to provide a multilayer plastic bottle having a layer of EVOH, to provide oxygen and CO2 barrier protection, that is approximately 2-3 mils thick.
It is another object of the invention to provide a multilayer plastic bottle having a middle layer of EVOH that has a varying thickness whereby the thickness of the EVOH layer has an even distribution of EVOH throughout the top and middle sections of the body of the bottle and which tapers from the middle section of the bottle to a thinner layer of EVOH at the bottom of the bottle.
It is another object of the present invention to provide a process for making a multilayer preform, which can be used to make a multilayer bottle, having a middle layer of EVOH that has a varying thickness whereby the thickness of the EVOH layer is evenly distributed throughout the top and middle of the body of the preform and tapers to a thinner layer of EVOH near the bottom of the preform.
It is still another object of the invention to provide a plastic bottle that is cost effective and provides good oxygen and CO2 barrier protection.
It is a further object of the invention to provide a container which provides improved ultra violet light protection for materials filled in the container.
It is still further an object of the invention to provide a bottle that has a thick layer of EVOH protection and still has a good, strong bottom profile.